Why do some mass killers write/inscribe writing on their guns or gear?

The very first instance I can think of this occurring in mainstream shootings was Aaron Alexis, the perpetrator of the DC Navy Yard shooting who had inscribed several phases on his Remington 870 shotgun, warning about low electromagnetic frequencies controlling his brain, describing it as a defensive weapon and other typical paranoid schizophrenic messaging on it.

After this, I believe it was used primarily by right wing shooters with Neo-nazi viewpoints. -Brenton tarrant, multiple writings about immigrants, historic battles between Christians and Muslims, famous deaths of white people by immigrants, and memes. Also writing on mags, speakers, not just guns.

-Peyton Gendron (clearly inspired, if not a copycat of Tarrant) paying homage to other mass shooters such as Tarrant, Breivik, Bowers. Also wrote racial slurs and memes on the guns.

-Ryan Palmeter (also right wing) and inspired by these other shooters follows a similiar path with memes, slurs and racially motivated attacks written on the guns.

And I believe most recently the 17 year old boy in Nashville also write on his magazines.

My question is why— does it provide more of a statement writing these things on the actual weapon of choice used in the massacre? Do they feel as if they get more publicity or notice from this versus simply publishing a manifesto online or in chat rooms before an attack?

Or this is more so as a result of Tarrant setting an example and many choosing to copycat his actions, and spread notoriety through these actions? Just something I thought of recently.